In the 3rd generation partnership project (3GPP), a carrier aggregation (CA) technology is introduced, so that user equipment (UE) supporting the carrier aggregation technology can send or receive data on more than one component carrier within one transmission time interval, thereby improving a peak rate of the user equipment. In a case of carrier aggregation, multiple pairs of system-associated carriers may be included, where a pair of system-associated carriers denote paired downlink and uplink carriers, that is, carriers corresponding to signaling connection and notification in a system information block 2 (SIB2), and may be considered as a serving cell, the downlink carrier of the system-associated carriers may be considered as a downlink carrier corresponding to the serving cell, and the uplink carrier of the system-associated carriers may be considered as an uplink carrier corresponding to the serving cell. However, some UEs having no carrier aggregation capability also exist in a system, and this type of UEs cannot receive and/or send data on more than one carrier at a same moment, where having no carrier aggregation capability includes: having no carrier aggregation capability on a downlink, having no carrier aggregation capability on an uplink, or having no carrier aggregation capability on both an uplink and a downlink.
On each serving cell and a carrier corresponding to the serving cell, a quantity of user equipment and service distribution are time-variant to some extent, and channel quality of user equipment on each serving cell and a carrier corresponding to the serving cell is also time-variant. After being connected to a base station, user equipment having no carrier aggregation capability can operate only on a time division duplex (TDD) carrier or a pair of system-associated frequency division duplex (FDD) carriers; therefore, channel quality of the user equipment is also affected by a load of this carrier or carrier pair and often changes, causing relatively bad user experience. The present invention provides a carrier switching method, so that user equipment having no carrier aggregation capability can dynamically perform switching between carriers and perform data transmission between the carriers, so as to better match service distribution and dynamic change of channel quality within each carrier, thereby obtaining better system performance and user experience.